Valve-regulated lead acid (VRLA) batteries, which are typically vented batteries with electrolyte suspended between the electrodes, are known in the art. They may provide certain advantages over flooded lead acid batteries (by way of example only, free-flowing electrolyte) while they may possess certain disadvantages compared with flooded batteries (by way of example only, they may take 3-10 times longer, or more, to fill with acid than counterpart flooded batteries and they may be more expensive than flooded batteries, since they may contain, for example, more lead). When VRLA batteries are filled with acid, the acid is injected to cover the electrodes and this may be done, in some instances, under vacuum or reduced pressure (possibly to ensure uniform acid filling).
Some VRLA batteries are known as VRLA-AGM batteries, meaning that the separator used in such batteries may include one or more layers of an AGM (absorptive glassmat or absorbed glass mat). Depending on VRLA-AGM battery design, up to 2-4 attempts, or more, may be needed to fill a VRLA-AGM battery with acid, compared with filling a counterpart flooded battery, which might require only one acid filling event or step or attempt. It is important to fill batteries with acid as quickly as possible in order to decrease production time (and therefore production cost) but also to preserve the quality of the battery. This is because, as batteries are being filled with acid, the acid can react with unformed plates and turn to water, thereby solubilizing lead and potentially leading to shorts, such as hydration shorts. Thus, acid filling needs to be uniform and quick, such that a battery manufacturer can complete the steps of battery formation and charging as quickly as possible and maintain high quality for the battery.
Various battery separators for VRLA batteries are also known in the art. As mentioned above, users might employ one or more layers of an AGM (absorptive glassmat or glass mat) as the separator with VRLA batteries. Such AGM layers may be made of glass fibers, polymeric fibers, or a combination thereof. An AGM layer may absorb battery acid like a sponge or act as an acid reservoir, immobilizing the acid, and such AGM layers may perform well in the acid-limited or acid-starved system, which is also under compression. However, the glass fibers in AGM separators may break over time during cycling and under high compression. The degradation of the glass fibers may change the level of compression in the battery system over time and may influence acid migration within the AGM separator, possibly resulting in poor acid availability to the electrodes and/or potentially leading to acid stratification. Acid stratification in a VRLA battery may lead to underutilization of a portion of the electrodes potentially resulting in sulfation, poor battery performance, and/or short or shorter cycle life. Additionally, while acid-filling a VRLA battery using a traditional AGM separator, an electrode may become more reactive, consuming acid and/or converting it to water or steam, which can create lead sulfate and can lead to hydration shorts, dendrite growth, battery life reduction, dry spots, and/or thermal runaway. The last regions of the AGM separator to be wetted by the electrolyte are the most prone to risk of hydration shorts.
In some instances, such as in U.S. Pat. No. 6,703,161 owned by Daramic, LLC of Charlotte, N.C., and incorporated by reference herein, there have been disclosed battery separators for lead acid storage batteries that are, for instance, multi-layer battery separators, and such separators may be used with VRLA batteries.
VRLA batteries may also, in certain instances, be described as “gel” batteries, and they include a battery separator as well as fumed silica in the electrolyte that immobilizes the electrolyte or acid and turns the electrolyte or acid into a gel. In some instances, VRLA gel batteries may provide certain advantages, such as, for example, higher capacity, deeper cycling, and/or more robust performance. Still other batteries are hybrid VRLA AGM and gel (sometimes called faux-gel) batteries that may include an AGM separator with gelled acid on the top of the cell or some fumed silica inside the AGM separator or in the acid or in the system, so that the system does not dry out.
There is a need to further develop even more improved battery separators for all types of VRLA batteries (including AGM, gel, and those batteries, sometimes called hybrid VRLA AGM batteries, that combine aspects of AGM and gel).